Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

the thermostat that came in my home was ancient, so i replaced it with a common Honeywell digital stat from the local hardware store. ever since then, the fan kicks on and off twice quickly after the heat shuts off under normal circumstances. this only happens in heat mode. i tried a different thermostat claimed to work with 99% of systems and got no change.

i have four wires. one of them is blue, which i hook up to the yellow stat socket 'cos that seems like the obvious choice. i'm wondering if this logic is the problem.

The thermostat is likely not the cause of the problem. If you have an older natural draft gas furnace, the fan limit may be cycling from residual heat off the heat exchanger after the thermostat satisfies and shuts the gas off.

Either that or the thermostat is controlling the fan rather than the furnace and is shutting the fan off when the gas valve closes. This will definitely cause the furnace to cycle on limit.

I have installed 1 honeywell t stat that turned fan on as sone as it called for heat as far as the blue wire on y if it was on y before then yes other wise you have to check where it goes y is for a/c condencer

Hmm,

If a guy tells me that he put the blue wire on th Y terminal I would think that there was no yellow wire in the cable and if he said that that was the obvious thing to do I wouldn't think that he was a moron because he knew when he took the wire off the old one that the blue one was used and that the Y terminal was used I would have to say that he probably has it wired right and is stuck on the problem that his furnace short cycles now, the most obvious reason for this is that the temperature at the stat is changing that quickly If thats the case you will need to either move the air flow or the stat.

You may not have noticed it on the mechanical stat because the anticipator was set at a high setting to compensate for the problem. If you go into your manual for the stat they have an anticipator like function that allows you to set the maximum amount of cycles per hour your furnace can run. Although none of this means anything if you were trying to fix a problem with your furnace by changing the stat.